As described in U.S. Pat. No. 6,633,254 issued to Eldon Sutphin, assigned to the assignee hereof and incorporated herein by reference, in the past, low-powered radar systems have been employed for use in intrusion alarms, vehicle sensing, surveillance and through-wall detection.
In one application, a CW radar is utilized to project energy through a wall and into a room where it is returned by moving objects such as an individual. The reflected energy from the moving object is indicated by a phase variation between the incident radiation and the reflected radiation such that, by measuring the phase difference of signals transmitted by the antenna and signals received by the same antenna, one can detect the presence of an individual in a room.
Systems employing such radars can also be adapted to provide an indication of not only the existence of a moving individual, but also the range of the individual to the particular radar involved. Moreover, such CW radars can be used with antennas at differing positions to be able to more accurately locate an individual and, for instance, to discriminate between individuals who move and stationary articles within a room.
The ability of small lightweight radars to penetrate walls is useful, for instance, in detecting individuals in a burning building or to conduct surveillance on individuals, both for police work and for military purposes.
In such applications, it is oftentimes necessary to have the individual manning the radar equipment to be removed from the radar itself for a number of reasons. One reason is that heat or other radiation from a building may be such as to preclude the presence of an individual manning the radar at the site.
Secondly, it may be desirable to have the individual manning the radar removed from the site due to, for instance, hostile actions taken when the individual is at the building. Also, covert operations require that the individual manning the radar be remote from the sensing location so as to remain undetected. Also, for motion detection-type radars, having an individual adjacent the radar may result in false alarms due to the individual being in the back lobe of the radar antenna. In such a case the radar may detect the movement of the individual manning the radar as opposed to movement of an individual within a building or within the main lobe of the radar beam.
For intrusion alarms, vehicle sensing and other surveillance applications, it is thus important to have an unmanned radar and to be able to monitor the results of the radar surveillance at a central location removed from the point at which the radar measurements are taken. Thus, for instance, if one wants to use multiple radars to surveille a given area, it is important to be able to have the radars communicate with a central location so that the individual radars need not be manned. Additionally, when radars are moved by robotic systems to be able to accurately pinpoint individuals within a building, oftentimes it is a requirement that the individual control the robot from a distance. This being the case, the radar returns must be displayed and/or analyzed at some distant point.
The aforementioned patent performs the communications functions but does so by continuously projecting the CW wave. The remote signaling is accomplished by modulating the frequency of the continuous wave. The result is that remote receivers used to monitor the radar returns must remain on continuously. This results in unnecessary power drain for these battery-powered receivers. Moreover, receivers oftentimes receive garbled transmissions if more than one radar is used, for instance, to improve on range measurements or to triangulate on a moving individual. Thus in the past there was no convenient way to separate out signals from multiple radars, much less specifically code returns from a given radar, either to address only a particular receiver or to provide a serial digital message.
Also, when attempting to monitor movement, it would be convenient if the multiple radars could communicate on a single communication channel. Since the radars would normally be operating on different frequencies or channels, it would be advantageous to be able to switch these radars to a single frequency for communications.
There is therefore a need to be able to address different remote receivers, like pagers, and to be able to convey information about detected movement without having to use a separate transmitter at the radar.